Apparatus for controlled electric discharge devices



14, 1933' c. E. KENTY 2 V APPARATUS FOR CONTROLLED. ELECTRIC DISCHARGE DEVICES Filed Jan. 15, 1935 V4 8 5 INVENTOR TO NEY Patented Jan. 14, 1936 UNITED STATES PATENT OFFICE APPARATUS FOR CONTROLLED ELECTRIC DISCHARGE DEVICES Application January 15, 1935, Serial No. 1,970

8 Claims.

The present invention relates to electric gaseous discharge devices generally, and more particularly to discharge devices of the type which are operated with a relatively constricted are.

A particular object of the invention is to provide a novel means for controlling the arc path within a discharge device in order to prevent the are from impinging on the envelope wall. A further object of my invention is to produce a magnetic field having a controlled rapidly decreasing intensity within such a device. Another object of my invention is to provide suflicient variation in the magnetic field along the arc path to maintain said are substantially straight throughout its length. Another object of my invention is to lessen the variation in arc position during the starting period of the device. Still another object of my invention is to produce these novel results without increasing the total wattage of the device. Still other objects and advantages of my invention will appear from the following detailed specification, or from an inspection of the accompanying drawing.

The inventionconsists in the unique combination of elements which is hereinafter set forth and claimed.

In operating gaseous electric discharge devices, such as the recently developed high intensity mercury vapor lamp, wherein there is a constricted arc discharge, difficulties are encountered whenever an attempt is made to operate the device with the are extending in other than a vertical line. These difilculties are caused by the fact that the arc tends to rise, due to the heating of the gas in the arc stream, and thus curves toward and impinges upon the upper wall of the arc tube as the latter is moved toward a horizontal position. The glass which is commonly used for these are tubes is not adapted to withstand the ensuing severe localized heating and hence softens, allowing the tube to lose its shape, and at the same time evolves copious amounts of gas into the discharge path, either of these effects alone being enough to ruin the discharge device.- It has been proposed heretofore to overcome this difliculty by the use-of a magnetic force which opposes this tendency toward upward movement of the arc stream, and in practice it has been found that this gives very desirable results. A lesser difficulty still remains however. Thus during the starting period of one of these high intensity mercury vapor arc lamps the arc current is quite high, of the order of double that which flows after the vapor pressure has reached equilii rium, and hence the series magnets which are necessarily used exert a downward force on the arc which isof the order of four times that which is exerted during normal operation of the lamp. At the same time the temperature of the arc stream is still less than that attained during 5 operation, so that the gravitational forces which tend to force the arc upwardly are much less than those which the magnetic force is designed to neutralize. As a result it is found that a magnetic field which is entirely satisfactory during 0011- 10 tinued operation of a lamp will force the arc downwardly onto the lower wall of the arc tube during starting, failures occasionally occurring as the result of the abnormal heating to which the envelope wall is thus subjected.

Another difiiculty which has been heretofore encountered results from the fact that for some reason which is not entirely understood the ends of the are, adjacent to the electrodes, are forced upwardly more strongly than the middle of the are, with the result that in any uniform magnetic field the arc assumes a somewhat bowed shape with a reverse curve in the middle. In certain types of reflectors this is undesirable since it reduces the efficiency of the reflector, due to the deviation of the are from a straight line source.

I have now discovered that both of these difficulties are overcome by the use of a novel magnet structure of my invention, which provides a field which not only decreases rapidly within the lamp but also varies along the arc path in a manner which compensates for the unequal thermal forces on various parts of the are. This novel magnet structure, which is a modification of the structure disclosed in my co-pending application, Ser. No. 746,726, filed October 3, 1934, consists in a coil having a core which produces a substantially uniform field of steep gradient along the arc path, plus an additional core which is shorter than the first mentioned core and which not only increases the steepness of the field gradient but also decreases the field intensity within its zone of influence. With this novel structure I have found that the rapid reduction in field intensity below the axis of the arc tube greatly minimizes the depression of the arc during the period of high current flow at starting. Furthermore the variation in the magnetic field along the arc path is sufiicient to compensate for the variation in the forces tending to move. said are upwardly, so'that the arc is maintained in a substantially straight line at the axis of the arc tube. The steep field gradient also assists in maintaining the are substantially straight since it virtually eliminates the effects of any slight t5 deviation from an exact compensation for variations in the thermal forces exerted on.difierent parts of the arc.

Where it is desired to still further limit the variation in position of the arc during the starting period I have found that the use of a saturable core for my novel magnet or of a series transformer with a saturable core very materially aids in reducing the magnetic force during the continued flow of the high starting current.

All of these novel results are obtained through the use of a series coil which materially assists in the necessary stabilization of the are, so that no additional energy is required therefor. An additional advantage of my novel structure is that it readily lends itself to inclusion within a reflector which is mounted close to said lamp.

For the purpose of illustrating my invention I have shown in the accompanying drawing a preferred embodiment thereof.

In the drawing Fig. 1 is an elevational view of a complete lamp unit embodying my invention,

Fig. 2 is a sectional view of this unit taken on the line 2--2 of Fig. l, and

Fig. 3 is an eievational view of the magnet structure.

As shown in the drawing my novel lamp unit consists of a high intensity mercury vapor arc lamp I of the general type disclosed, for example, in the co-pending application of James A. St. Louis, Ser. No. 724,586, filed May 8, 1934, which is screwed horizontally into a suitable socket (not shown) within the housing 2, together with the V-shaped reflector 3 which is supported by said housing with the angle in said reflector extending along said lamp, and virtually in contact therewith. This reflector, which is made of brass, aluminum, or other non-magnetic sheet metal, is designed to reflect the light from the lamp I in a horizontal direction or slightly below, the unit thus being especially suited for street lighting and other uses where an extremely broad distribution of light is required. A magnet core 4, which is conveniently formed of inch sheet iron or any other suitable magnetic material bent into the form of a channel with converging sides, the gap between these sides being of the order of 2 or 3 millimeters, is positioned in the angle of the reflector 3 with the air gap therein as near the bottom of said reflector as it will go, and extends longitudinally to a point somewhat beyond the electrodes within the inner arc tube 5 of the lamp I, as indicated by the lotted lines in Fig. 1. A coil of wire 6 is wound longitudinally on the core 4, fifty to sixty turns ordinarily being employed. A second core 1, of similar shape to the core 4, is placed above the coil 6 with the edges thereof extending downwardly and slightly overlapping the sides of the core 4, preferably with an air gap of the order of a few millimeters therebetween. A plurality of ears 8 which are formed in the core 'I are bent inwardly and welded to the core 4, and thus serve to maintain the desired relationship betwen said cores, while the ears 9 on the core 4 are used to support the entire magnet structure in the desired position with respect to the reflector 3. As clearly shown in Fig. 3 this core 1 extends for only a short distance along the coil 6, say for the middle three inches where the arc path in the lamp I is six inches long. It is in this feature that the present structure principally departs from the structure disclosed in my co-pending application, Ser. No. 746,726, flied October 3, 1934. I have found that this second core not only intensifies the gradient with which the field decreases with distance from the gap in the core 4, but that it also weakens the fleld produced by the coil 6. I have furthermore discovered that the field gradient does not need to be so steep in the neighborhood of the electrodes as it is along the rest of the arc path. Hence by limiting the core I to the central portion of the core 4 I have produced the double result that the gradient is made the steepest at 10 the point where a steep gradient is needed, and at the same time the field is weakened at the very point where a weaker field is necessary in order to avoid bowing of the are. For best results this core 1 should not extend as close to the lamp I as does the core 4. The coil 6 is connected in series with the arc in the lamp I, the connection being such that the current flows in the coil 6 above the core 4 in the same direction as in the arc itself at any given moment. An inductance 20 (not shown) which cooperates with the coil 6 in stabilizing the operation of the arc, is enclosed within the housing 2. Lead wires III extend into said housing from any suitable source, prefer ably 220 volts A. C. For best results the gauze 2:, band I2 on the arc tube 5, which serves as a starting electrode, should be made of a nonmagnetic material, so as to avoid any magnetic shielding of the enclosed portion of the arc.

with the structure which has been described 30 as soon as potential is applied to the leads III an arc is immediately initiated within the arc tube 5, this are current flowing in series through the coil 6. At the moment of starting, this current is of the order of double the normal oper- 3 ating current of the lamp I, due to the low vapor pressure of the mercury within the arc tube 5. As a result the magnetic field produced by the coil 6 is likewise doubled, and the magnetic force which would be exerted thereby on the are 40 stream at the axis of the arc tube therefore quadrupled. The fleld due to the coil 6 falls of! extremely rapidly with increases in the distance from the apex of the reflector 2, however, the core 4 being so shaped as to accentuate this char- 45 acteristic, and in order to utilize the steepest portion of the field gradient said core is preferably located as close to the lamp I as possible. The core I forms a sort of magnetic shunt for a portion of the core 4, and has been found to re- 60 suit in a slightly weakened fleld in the lamp I and in addition to produce a marked increase in the rapidity with which said field decreases with distance from the core 4 within the zone of influence of said core 1. Due to the steep gradient 5'1 in the field intensity which is thus produced it is obvious that only a slight shift in the arc position is necessary to completely compensate for the effects of this large starting current, so that even under these adverse conditions the are still 60 operates close to the axis of the arc tube. As a result there is no possibility of the arc impinging during starting upon the wall of this are tube. As the lamp I warms up-the vapor pressure therein rapidly increases, as is well known, and the arc current decreases until finally equilibrium is attained. At the same time the temperature of the gas in the arc stream increases, and this results in anincreased tendency for the arc stream to rise. As a result the arc stream gradually moves slightly upward within the arc tube 5 from its original position toward the center of the tube, until equilibrium is attained with the are operating exactly at the center of the tube, or slightly below, 1: it is desired to equalize the top and bottom temperatures of the'arc tube 5.

The steepness of the field gradient which results from my novel magnet structure is of great assistance in holding the are at the desired central point during continued operation, since any upward deviation of the arc results in a vast increase in the magnetic force exerted, while a downward deviation results in a correspondingly decreased force, making the position of the arc quite critical. Hence such a gradient is desirable both during starting and continued operation of the discharge device, since it always maintains the arc within a limited zone close to the axis pf the tube 5. This steep gradient is also of advantage in another respect, however. The arc in the arc tube has an unequal tendency toward upward movement at different points along' the arc. Thus in the vicinity of the electrodes this force is greater than at the middle of the arc. As a result the arc tends to bow upwardly near the ends and downwardly near the middle when a uniform magnetic force is applied thereto to keep it at the center of the arc tube. With my novel structure this bending of the arc is completely eliminated, due not only to the fact that the field strength is varied to compensate for this variation in the upward forces, but also to the fact that the rapid changes in field strength with slight changes in position minimize the amount of bowing necessary to overcome any slight deviations from an exact balance in the forces at the axis, with the result that the arc in my novel outfit is free of any observable bowing. I

In case it is desired to further reduce the depression of the arc during starting the core 4 is made saturable by the starting current by reducing the thickness thereof or in any other suitable manner. Likewise, a circuit in which a saturable transformer is employed may be used for this purpose, as disclosed in the co-pending application which has been hereinbefore referred to. still eifectively in series with the device I, and the claims are to be so construed.

From the foregoing it will be'apparent that the important feature of my invention is the use of a magnetic field with a varying intensity along the arc path and with an extremely steep gradient within the arc tube of a high intensity vapor arc lamp to confine the ar c at all times to a straight line path within a limited zone near the axis of said are tube.

While I have illustrated my invention by reference to certain specific structures which I have found to produce successful results it is obvious that my invention is not limited thereto, but that various changes, omissions and substitutions, within the scope of the appended claims, maybe made therein or in the mode of operation without departing from the spirit of my invention.

I claim as my invention:

1. In combination, an electric gaseous discharge device comprising a sealed envelope containing a gaseous atmosphere and having electrodes sealed therein, and means to produce a magnetic field within said device to control the position of an are between said electrodes, said means comprising a magnet coil traversed by a current which is a function of the discharge current within said device, a core for said coil which tends to produce a field within said device which is substantially uniform along the arc path between said electrodes but which has a steep gradient in a direction normal thereto, and

In the latter case, of course, the coil 6 is second core for said coil which weakens the field produced within said device by the first mentioned core and which increases the gradient thereof, said second core being confined to the central portion of said are path.

2. In combination, an electric gaseous discharge device comprising a sealed envelope containing a gaseous atmosphere and having electrodes sealed therein, and means to produce a magnetic field within said device to control the position of an are between said electrodes, said means comprising a magnet coil connected in series with said device, a core of magnetizable material extending through said coil and then converging to form an air. gap which extends along said device beyond each of said electrodes parallel to the desired arc path, and a second core which extends about one side of said coil and overlaps the first mentioned core on either side of said coil, said second core being limited to the central portion of said arc path.

3. In combination, an electric gaseous discharge device comprising a sealed envelope containing a gaseous atmosphere and having electrodes sealed therein, and means to produce a magnetic field within said device to control the position of an are between said electrodes, said means including a magnet coil connected in series with said device. a core of magnetizable material extending through said coil and then converging to form an air gap which extends along said device beyond each of said electrodes parallel to the desired arc path, and a second core which extends about one side of said coil and overlaps the first mentioned core on either side of said coil with a small air gap therebetween, said second core being limited to the central portion of said are path.

4. In combination, an electric gaseous discharge device comprising a sealed envelope containing a gaseous atmosphere and having electrodes sealed therein, and means to produce a magnetic field within said device to control the position of an arc between said electrodes, said means comprising a magnet coil which is connected in series with said device and which extends longitudinally thereabove, a core extending through said magnet and having downwardly extending portions which converge to form an air gap which extends just above said device throughout the distance between said electrodes, said coil being so connected that the field therefrom tends to force the arc stream downwardly in said device, and a second core for said device which weakens the field produced by the first mentioned core within said device and increases the gradient of said field normal to the path of said arc, said second core being limited to the central portion of said arc.

5. In combination, an electric gaseous discharge lamp comprising a sealed envelope containing a gaseous atmosphere and having electrodes sealed therein, the arc path between said electrodes being substantially horizontal, a reflector of non-magnetizable material mounted above said lamp, said reflector having converging sides with an apex virtually in contact with said lamp, a magnet coil within the converging sides of said reflector, a core of magnetizable material passing through said coil and having downwardly extending portions which converge within said apex to form an air gap which extends along said lamp beyond the electrodes at either end thereof, and a second core for said acoil which extends above said coil and then down- 7 wardly on either side thereof to slightly overlap the first mentioned core, said second coil being limited to the central portion oi the path between said electrodes, whereby an arc therebetween is maintained substantially straight.

6. In combination, an electric gaseous discharge device comprising a sealed envelope containing a gaseous atmosphere and having electrodes sealed therein, and means to produce a magnetic field within said device to control the position of an are between said electrodes, said means including a magnet coil connected in series with said device, a core for said coil which tends to produce a field within said device which is substantially uniform along the arc path between said electrodes but which has a steep gradient in a direction normal thereto, saturable means to reduce the ratio of the strength of said field to the arc current when said current is above the normal equilibrium value, and a second core for said coil which weakens the field produced within said device by the first mentioned core and which increases the gradient thereof, said second core being limited to the central portion of said are path.

'7. In combination, an electric gaseous discharge device comprising a sealed envelope containing a gaseous atmosphere and having electrodes sealed therein, and means to produce a magnetic field within said device to control the position of an are between said electrodes, said means including a magnet coil connected in series with said device, a core for said coil which tends to produce a field within said device which is substantially uniiorm along the arc path between said electrodes but which has a steep gradient in a direction normal thereto, said core being saturable by a current slightly in excess of the current flowing through said device when it is in a condition of equilibrium, and a second core for said coil which weakens the field produced within said device by the first mentioned core and which increases the gradient thereof, said second core being limited to the central portion of said are path.

8. In combination, an electric gaseous discharge device comprising a sealed envelope con taining a gaseous atmosphere and having electrodes sealed therein, and means to produce a magnetic field within said device to control the position of an are between said electrodes, said means including a magnet coil connected in series with said device, and a core for said coil which produces a field within said device having a steep gradient in a direction normal to the path of a discharge between said electrodes, said core being saturable by a current slightly in excess of the current flowing through said device when it is in a condition of equilibrium.

CARL E. KEN'I'Y. 

